Generally a fuel cell unit which generates electrical power is provided as a stack of a plurality of fuel cells. During power generation, heat is generated from the fuel cells. To cool the fuel cell unit, a cooling plate is inserted between every few fuel cells.
A fluid path for coolant is provided in each cooling plate in order to cool the fuel cell unit.
A coolant for a fuel cell unit circulates within the stack of the fuel cells and cools the fuel cells. If the electrical conductivity of the coolant is “high”, the electricity generated in the fuel cells partially flows into the coolant, resulting in loss of electrical power generated in the fuel cell unit.
Conventionally, pure water which is very low in electrical conductivity and thus high in electrical insulation has been used as coolant for fuel cell units.
In the case of a fuel cell system which is used intermittently, such as a fuel cell system for an automobile, the temperature of the coolant is subject to the atmospheric temperature when not in use. When the atmospheric temperature falls below the freezing point, pure water coolant would freeze, potentially leading to physically damaging the cooling plates. The battery performance of the fuel cell system would then deteriorate.
Accordingly, low electrical conductivity and good antifreeze property are required of coolant for fuel cell systems, especially for fuel cell systems of automobiles.
A coolant composition containing a base component of a water-glycol blend and an amine based alkaline additive that works to maintain the electrical conductivity of the coolant low has been proposed (see Japanese Unexamined Patent Publication 2001-164244).
Such a glycol may be oxidized during use, and may produce ionic substances. Such ionic substances raise electrical conductivity of the coolant.
The coolant paths of a fuel cell system are generally provided with an ion exchanger or ion exchange resin to remove such ionic substances.
However, the capacity of the ion exchanger deteriorates as time goes by because the ion exchanger is “consumed” for removal of the ionic substances.
Accordingly, it is an object of the present invention to provide an anti-freeze coolant composition for a fuel cell unit, which is capable of maintaining the electrical conductivity of a coolant low for a long period of time by suppressing generation of ionic substances in the coolant.